The present invention relates to automated and automatic mechanical transmissions for motor vehicles and, more particularly, to an apparatus and method for converting a transmission from one operating configuration to another operating configuration. The operating configurations may utilize fewer than the maximum number of available transmission gear ratios. Other transmission characteristics can additionally be changed to result in a new operating configuration.
Engine manufacturers have been modifying and increasing power ratings of existing engines while transmission manufacturers, in general, have not modified the corresponding transmissions that mate with those engines. As a result, transmission components, such as gears, shifters, input and output shafts, all have increased loading. Moreover, an engine having an increased power rating that is coupled to a transmission designed for lower power ratings diminishes overall efficiency and decreases transmission service life.
Automatic and automated transmissions are known for use in motor vehicles and have the ability to perform gear shifts without driver intervention. Gear shifting is typically performed by hydro-mechanical or electro-mechanical devices and is based on characteristics such as engine speed or throttle position. Transmissions that are electronically controlled by a programmable computer are also known. Some transmissions are able to modify their shift points in response to a request for greater fuel efficiency or more power. The transmissions may have two sets of shift points, one set for fuel efficiency and a second shift point set for more power to improve starting or load carrying capability. Thus, shifting of the transmission may be modified depending on the needs of a vehicle operator. Still further, it is known to adjust the gear shift points by considering operating conditions such as grade and load. See for example, U.S. Pat. Nos. 5,479,345 and 5,416,700, the disclosures of which is hereby incorporated by reference.
However, the previously known automatic or automated transmissions do not permit a vehicle operator to change the overall operating characteristics of the transmission. For example, the previous transmissions do not allow changing a transmission for use in an 18 speed highway tractor trailer to be used instead in a 10 speed local delivery dump truck.
In addition, the prior transmissions do not permit an operator, repairman or even the transmission itself to selectively eliminate a gear from the set of available transmission gears upon excessive wear or damage to that gear. Further, the prior art does not permit a reorganizing of remaining available gears to smoothly make up for a gear that is eliminated.
The present invention is directed to a convertible transmission system for a vehicle comprising a transmission having an input shaft for connection to an engine and an output shaft for delivering rotational power to at least one axle. The transmission has a plurality of available gear ratios resulting in a maximum number of available gear ratios. In addition, a programmable controller is provided for selectively controlling the transmission to operate in a first operating configuration utilizing a first predetermined number of the available gear ratios that is less than the maximum number of available gear ratios.
In accordance with the present invention, the programmable controller can provide for selectively controlling the transmission to operate in a first operating configuration utilizing a first predetermined number of the available gear ratios and a second operating configuration utilizing a second predetermined number of the available gear ratios. The first predetermined number of the available gear ratios can be greater than, less than, or equal to the second predetermined number.
The first and second operating configurations can optionally include respective first and second predetermined maximum torque limits, for each of the available gear ratios and/or first and second predetermined shift point patterns and/or shift strategies and/or predetermined coast down gears and/or default starting gears.
The convertible transmission system of the present invention optionally includes the first and second operating configurations respectively having first and second predetermined sets of forward gear ratios and/or sets of reverse gear ratios selected from the available gear ratios.
Further, the first and second operating configurations optionally respectively include first and second predetermined shift delay timing.
In addition, the first predetermined number of available gear ratios can be any number, for example, 18 and the second predetermined number of available gear ratios can be a positive integer equal to or less than the first predetermined number, including, for example, 7, 8, 10, 12, 13 or 15.
The convertible transmission system of the present invention has the ability to use a second operating configuration that skips or eliminates a predetermined shift that was present in the first operating configuration because an original one of the available gear ratios is no longer available due to gear wear or gear failure. Further, the second operating configuration can include at least one of adjusted torque limits and adjusted shift points to compensate for gear wear or gear failure.
According to one embodiment of the present invention, the programmable controller controls the transmission to operate in a first operating configuration utilizing the maximum number of available gear ratios and a second operating configuration utilizing less than the maximum number of available gear ratios. In addition, the second operating configuration can include at least one of adjusted torque limits and adjusted shift points to compensate for gear wear.
The present invention is also directed to a method of operating a transmission having a plurality of available gear ratios resulting in a maximum number of available gear ratios comprising the steps of: selecting a first predetermined set of desired gear ratios from the plurality of available gear ratios for establishing a first transmission operating configuration and determining a change in at least one operating condition that necessitates selecting a second predetermined set of desired gear ratios from the plurality of available gear ratios for establishing a second transmission operating configuration. The at least one operating condition can be a vehicle operator""s desire for improved performance, excessive gear wear or gear damage, and/or an expected vehicle application (e.g. a dump truck or tractor trailer application).
Therefore, the present invention provides a transmission system that permits a vehicle operator to change the overall operating characteristics of the transmission. For example, the same transmission can be re-configured for use in an 18 speed highway tractor trailer or a 10 speed local delivery dump truck. The present invention permits a same transmission having a maximum number of available gears to be utilized as if the transmission had been designed and manufactured with fewer gears.
In addition, the transmission system of the present invention permits an operator or repairman to selectively eliminate a gear from being selected from the set of available transmission gears when excessive wear or damage to that gear is discovered. Further, the present invention permits a reconfiguring of remaining available gears, shift strategy, default starting gear, reverse gears, forward gears, torque limits, and/or shift points to smoothly compensate for the gear that was eliminated because of wear.
Accordingly, the present invention allows a transmission manufacturer to have increased production volume of a single convertible transmission model instead of multiple lower volume non-convertible transmission models resulting in production efficiencies and lower manufacturing costs. Vehicle manufacturers and repair facilities can order and stock a single convertible transmission model rather than several different transmission models, which reduces inventory tracking costs and the rate of inventory turn-over.
Still further, a vehicle operator can efficiently change the transmission configuration as needed. For example, a vehicle operator may reconfigure the transmission to compensate for gear wear, driving through mountain roads, changing from city driving to highway driving. A convertible transmission can be modified when a vehicle is sold from a location having relatively flat city driving for use in highway mountain driving. Alternatively, the transmission can be re-configured if it was originally installed on a tractor trailer logging truck and then removed and installed on a cement truck that drives on flat city streets.
The increased weight of additional gears in a convertible transmission has the drawback of lowering fuel efficiency. However, the increased weight drawback is sufficiently offset by the increased efficiency of an automated transmission and the increased efficiencies in manufacturing and inventory control.